Array rotation for ultrasound catheters

ABSTRACT

A transducer array is connected with a catheter housing. As the transducer array is rotated, the catheter housing also rotates. As a result, at least a portion of the catheter housing twists about a longitudinal axis. By applying rotation in a controlled way, such as with a motor, a plurality of two-dimensional images for three-dimensional reconstruction may be obtained. The rotation of the catheter housing may limit the total amount of rotation of the array, such as rotating the array through a 90 degree or less amount of rotation about the longitudinal axis. The housing of the catheter is formed with a soft section. The softer material allows for a greater amount or increased ease for twisting the catheter.

BACKGROUND

The present invention relates to ultrasound imaging with catheters. Inparticular, two- or three-dimensional imaging is provided with an arrayin a catheter.

In the AcuNav™ catheter, a 64 element array of elements extends along alongitudinal axis of the catheter. The array is positioned at a tipportion for scanning a two-dimensional region or plane along thelongitudinal axis. Other catheters have been proposed where one or moreelements are rotated within the catheter about the longitudinal axis toscan in a plane perpendicular to the axis.

During use, a catheter is inserted within the circulatory system of thepatient. The flexibility along the catheter may vary as a function ofposition, such as having a more flexible tip portion for off-axisbending while guiding the catheter. The catheter is guided through thecirculatory system to position the ultrasound transducer adjacent to adesired location. Guide wires or rotation of the entire catheter areused to position the image plane at the desired location. Variousstresses and strains may cause bending and slight twisting along thecatheter. Images are then generated of the desired location.

By only scanning along a two-dimensional plane, identifying the desiredlocation may be more difficult. Three-dimensional imaging has beenproposed for more easily identifying a region of interest. Sincecatheters are small, such as having a 3 mm diameter, it may be difficultto position a two-dimensional array within the catheter.Three-dimensional imaging may be provided by moving the imaging plane ofthe one-dimensional array. For example, the catheter is slowly insertedfurther or withdrawn from a current position to create a plurality ofcross sectional scans using a rotating array. However, the imaging planeposition for accurate or higher resolution three-dimensionalreconstruction may be difficult.

BRIEF SUMMARY

By way of introduction, the preferred embodiments described belowinclude systems, methods and catheters for ultrasound imaging of avolume. Rotational forces are applied to a transducer array. Thetransducer array is connected with the catheter housing. As thetransducer array rotates, the catheter housing also rotates. As aresult, at least a portion of the catheter housing twists about alongitudinal axis. By applying rotation in a controlled way, such aswith a motor, a plurality of two-dimensional images forthree-dimensional reconstruction may be obtained. The rotation of thecatheter housing may limit the total amount of rotation of the array,such as rotating the array through a 90 degree or less amount ofrotation about the longitudinal axis. In one embodiment, the housing ofthe catheter is formed with a flexible or softer section. The softermaterial allows for a greater amount of or increased ease for twistingthe catheter.

In a first aspect, a catheter is provided for ultrasound imaging of avolume. A transducer section of the catheter houses an ultrasoundtransducer array. The array is connected with the transducer section. Amotor is spaced from the transducer section. A drive shaft connects themotor with the transducer section. A flexible section of the catheterconnects with the transducer section. The drive shaft extends through atleast a portion of the flexible section. The drive shaft is operable torotate the ultrasound transducer array and connected transducer sectionsubstantially about a longitudinal axis of the catheter in response toforce from the motor. The flexible section is operable to twist aboutthe longitudinal axis in response to the rotation of the transducersection.

In a second aspect, a system is provided for ultrasound imaging of avolume. A catheter has a housing. An ultrasound transducer array ofelements is within the housing. A shaft is also within the housing. Theshaft connects with the ultrasound transducer array of elements. Theultrasound transducer array is operable to rotate about a longitudinalaxis of the housing in response to rotation of the shaft. The housing isoperable to twist from a first portion to a second portion of thehousing. An amount of twist corresponds to an amount of rotation of theultrasound transducer array.

In a third aspect, a method is provided for scanning a volume with anultrasound catheter. A transducer array is rotated about a longitudinalaxis of the ultrasound catheter. A first portion of a housing of theultrasound catheter is also rotated about the longitudinal axis with thetransducer array. The transducer array and first portion rotate asubstantially same amount. A second portion of a housing twists aboutthe longitudinal axis in response to the rotation of the transducerarray, the first portion of the housing or both the transducer array andthe first portion. A third portion of the housing of the catheter ismaintained substantially free of the twisting and rotation of the secondand first portions during the twisting and rotation of the second andfirst portions.

The present invention is defined by the following claims, and nothing inthis section should be taken as a limitation on those claims. Furtheraspects and advantages of the invention are discussed below inconjunction with the preferred embodiments and may be later claimedindependently or in combination.

BRIEF DESCRIPTION OF THE DRAWINGS

The components and the figures are not necessarily to scale, emphasisinstead being placed upon illustrating the principles of the invention.Moreover, in the figures, like reference numerals designatecorresponding parts throughout the different views.

FIG. 1 is a side view of one embodiment of a catheter for ultrasoundimaging;

FIG. 2 is a side view of the catheter of FIG. 1 in a twisted position;

FIG. 3 is a flow chart of one embodiment of a method for ultrasoundimaging with a catheter; and

FIG. 4 is a cross-section view of one embodiment of a motor for rotatinga transducer.

DETAILED DESCRIPTION OF THE DRAWINGS AND PRESENTLY PREFERRED EMBODIMENTS

An ultrasound transducer stack within a catheter is rotated about thelongitudinal axis of the catheter for positioning a two-dimensionalplane at a desired location or generating a three-dimensional image. Amicro-motor or other source of force rotates the transducer stack. Whilea rotating joint may be used, seals and cable routing of a rotatingjoint are difficult to implement in a small space of a typical catheter.To avoid or limit these difficulties, the catheter housing is radiallydeflected to allow rotation of the transducer array. For example, ahousing of low durometer or soft Pebax is provided with a rigid shaft.The rigid shaft transmits force for rotation of the array. The softhousing allows twisting of the catheter about the longitudinal axis.

FIG. 1 shows a system for ultrasound imaging a region or volume fromwithin a patient. The system includes a catheter 10 and a controller 24.The controller 24 is positioned outside of, away from or within thecatheter 10. In one embodiment, the controller 24 is positioned withinan ultrasound imaging system connected with the catheter 10.

The catheter 10 is adapted for insertion within a circulatory or venoussystem. For example, the catheter 10 is about 5 mm or less in diameter.Larger or smaller catheters may be used. The catheter 10 includes asterile or other safe coating for use within a patient. One or moreguide wires or other structures for steering the catheter 10 may beprovided. In other embodiments, the catheter 10 is adapted for insertionthrough a portal or tube within another structure, such as a guidecatheter. Any now known or later developed catheter structures may beused, such as providing an elongated flexible tip with a narrowerdiameter than the main body of the catheter 10.

The catheter 10 includes a housing 11, a transducer array 18, a shaft 20and a motor 22. Additional, different or fewer components may beprovided, such as providing the motor 22 external to the housing 11 in ahandle. As another example, guide wires, ports, tubes, circuitry, signalcabling, or other now known or later developed catheter structure isprovided.

The housing 11 includes one or more sections 12, 14, 16. For example, atransducer section 12 connects to a motor section 16 through a flexiblesection 14. The transducer section 12 corresponds to a section of thecatheter 10 surrounding or associated with the transducer array 18.Similarly, the motor section 16 corresponds to a portion of the housing11 associated with the motor 22. The transducer and motor sections 12,16 may be of any length, such as less than, the same as or greater thanthe length of the respective transducer array 18 and motor 22. Thesections 12, 14, 16 are provided at a tip of the catheter 10, such as aregion 1-10 inches in length at a distal portion of the catheter 10 froma handle. In other embodiments, all, one or more of the sections has agreater or lesser length. The flexible section 14 extends over anydistance, such as a centimeter, an inch, inches, or the entire extent ofthe housing 11 away from the transducer 18.

In one embodiment, the housing 11 is the same for each of the differentsections 12, 14, 16. For example, each of the sections 12, 14, 16 areformed from a same extruded material, such as a polymer. Other now knownor later developed materials may be used. In other embodiments, thehousing 11 of the catheter 10 varies as a function of the section 12,14, 16. In one embodiment, 35 to 25 shore D Pebax, Nylon or Silicone isused. In other embodiments, the housing 11 of the catheter 10 varies asa function of the section 12, 14, 16. For example, the extrusion processis varied or the material used for the extrusion is varied as a functionof the sections 12, 14, 16. The flexible section 14 is formed from asofter material or the same material processed to be softer than theharder transducer section 12 and/or motor section 16. While representedas sharp distinctions between the sections 12, 14, 16 by thecircumferential lines in FIG. 1, the difference in hardness maygradually vary between the sections 12, 14, 16. The softer flexiblesection 14 provides a lower durometer portion of the housing 11. Inalternative embodiments, the flexible section 14 extends over the motor22, over all or a portion of the transducer 18 or is separate from both.The motor section 16 and/or the transducer section 12 may have a samesoftness or hardness as the flexible section 14, as each other or bedifferent.

The flexible section 14 is operable to twist about the longitudinal axisof the catheter 10 in response to rotation of the transducer section 12and the transducer 18. FIG. 2 shows the flexible section 14 twisting ascompared to the motor section 16 and the transducer section 12. Thetransducer 18 and transducer section 12 are shown rotated by about 45degrees. Twist lines are shown in the flexible section 14 associatedwith the 45 degrees of twisting. The twisting is shown just by theflexible section 14, but may extend into or through the motor section 16and/or transducer section 12. Where the flexible section 14 is softer ormore flexible than other sections 12, 16, a greater amount of twistingmay be provided in the flexible section 14 than the other sections. Thetwisting may occur from a point of first contact of the transducer 18with the transducer section 12 through to a point of contact orconnection of the motor 22 to the motor section 16 of the housing 11.Where the sections have similar flexibility, the amount of twisting inany one section 12, 14, 16 is based on the length of the section.

The amount of the twist corresponds to the amount of rotation of theultrasound transducer array. For example, where the ultrasoundtransducer array is rotated about the longitudinal axis by 8 degrees, 15degrees, 30 degrees, 45 degrees, 90 degrees, 180 degrees, 270 degrees orother amount, the twist absorbs or is rotated the same amount from thetransducer 18 and the portion of the transducer section 12 through tothe motor 22 and a portion of the motor section 16. Where the motor 22or the transducer 18 mounts to the housing spaced away from the motor 22or the transducer 18, the mounting location determines the range oftwist. The amount of twist is about the same since the motor 22 and thetransducer 18 connect with the housing 11.

The catheter 10 and associated housing 11 allow for angularrepositioning of the transducer array 18 about the longitudinal axis byabsorbing the rotation through twisting in the catheter 10. The amountof twisting is more than incidental. The motor 22 and shaft 20communicate intentional rotation to the transducer array 18 for rotationabout the longitudinal axis. The twisting is in addition to or otherthan twisting provided by rotating the catheter 10 on the handleexternally to the patient while the catheter 10 is within the patient.

The ultrasound transducer 18 is a one-dimensional array ofpiezoelectric, membrane or other now known or later developed acoustictransducers. Multidimensional, such as 1.25, 1.5, 1.75 ortwo-dimensional arrays may be used. The transducer array 18 includes aplurality of elements extending along the longitudinal axis of thecatheter 10. The elements may be spaced from the axis or centered on theaxis. As the transducer array 18 rotates about the longitudinal axis,the face of the transducer associated with the elements rotates. Theimaging plane associated with the transducer elements also rotates. Amechanical elevation focus is provided in one embodiment, but anacoustical window without mechanical focusing may be provided in otherembodiments.

The transducer array 18 connects with the transducer section 12 of thehousing 11. For example, the transducer array 18 and its associatedstack, such as backing and matching layers, are pressure fitted withinthe transducer section 12. Alternatively, bonding, riveting, bolts,clips or other attachment mechanisms substantially fixedly attach thetransducer array 18 to the housing 11. As the ultrasound transducerarray 18 or the transducer section 12 rotates, the connection providesfor the other of the transducer section 12 or the transducer array 18 toalso rotate. For example, force supplied by the motor 22 along the shaft20 applies direct rotational force to the transducer array 18, thetransducer section 12 or both for rotating both. The connection betweenthe transducer section 12 and the transducer array 18 may be direct orindirect, such as connecting a backing block or other support structureof the transducer array 18 directly to or through one or more othercomponents to the housing 11. The connection may allow some relativerotation or slippage of the transducer array 18 separate from ordifferently from the transducer section 12. For example, the ultrasoundtransducer array 18 is operable to rotate a few degrees within thehousing 11 before also forcing the housing 11 at the transducer section12 to rotate along the longitudinal axis.

The motor 22 is a micro motor, such as a servo, piezo, stepper,micro-brushless DC, or other motor. In one embodiment, the motor 22 issufficiently small, such as being 3 mm or less in diameter, for beingpositioned within the catheter 10. A gear box, such as a planetary gearhead having a 50 to 1 or other gearing reduction, is provided as part ofthe motor 22 or separate from the motor 22. The motor 22 is operable tocause rotation of the shaft 20. In one embodiment, the shaft 20 and themotor 22 are positioned in a central position along the longitudinalaxis of the catheter 10, but may be offset from the longitudinal axis.The motor 22 and associated gearing allow the application of sufficienttorque along the shaft 20 to rotate the transducer array 18 and causetwisting of the housing 11. The motor 22 is spaced from the ultrasoundtransducer array 18 by the shaft 20. In one embodiment, the total forceor torque applied by the motor 22 is matched to the resistance caused bythe twisting of the housing 11 such that the housing 11 limits the totalrotation of the transducer array 18. For example, the limitation may be360 degrees or less, such as 90 degrees, 20 degrees, 10 degrees or otherlimitation on rotation in a given direction from a neutral position. Inalternative embodiments, the motor 22 supplies sufficient torque but islimited by control of the motor 22 to avoid undesired wrapping ofinternal components about the shaft 20. Rotation beyond 360 degrees maybe provided.

FIG. 4 shows another embodiment of the motor 22. The motor 22 isconnected to a rotational speed reducing mechanism. Reduction inrotational speed may be useful for low torque or inaccurate angularpositioning motors 22. Part 44 of the shaft 42 is threaded to translaterotation into lateral motion of the wedges 40. The lateral motion istranslated back into rotation by the matched wedges 40. As the wedges 40connected with the threading move laterally, rotation about the sameaxis as the shaft 42 is induced in the matched wedges 40. With finethreads on the first part 44 and rotationally matched wedges 40, therotation is reduced several fold, but any amount of reduction may beprovided. Alternatively, a reduction gear box is used. In yet otheralternative embodiments, gearing, cams or other mechanisms convertrotation in one direction into a wobble or back and forth rotation.

Another embodiment uses a push-pull motor or solenoid. The lateralmotion of the motor 22 is translated into rotation by matched wedges,gearing, rotational connection or other mechanisms.

The shaft 20 is a drive shaft for transmitting torque from the motor 22to the ultrasound transducer array 18. The shaft 20 is metal, plastic,polymer, fiberglass, resin or other now known or later developed rigidor semi-rigid material. The shaft 20 extends through the housing 11,including the flexible section 14. The shaft 20 is more rigid than theflexible section 14 of the housing 11 so that the torque may betransmitted for rotating the transducer array 18 while the flexiblesection 14 twists. The shaft connects with the motor 22 directly, suchas being part of the motor, or indirectly through gearing. The shaft 20connects directly or indirectly to the transducer array 18, thetransducer section 12 or both.

The shaft 20 is operable to rotate the transducer array and theconnected transducer section 12 substantially about the longitudinalaxis of the catheter 10 in response to force from the motor 22. Usingcontrol of the motor 22 or torsional limitations to the twisting of thehousing 11, the ultrasound transducer array 18 is operable to rotateless than 360 degrees in one embodiment, but greater or lesserlimitations on rotations are provided in other embodiments. The shaft 20is free of direct connection to the housing 11 other than for connectionwith the transducer array 18 or in the flexible section 14. The housing11 may apply friction to the shaft 20 or may be spaced away from theshaft 20 using one or more bearings for allowing rotation.

The controller 24 is a processor, digital signal processor, applicationspecific integrated circuit, field programmable gate array, digitalcircuit, analog circuit or combinations thereof. The controller 24 isoperable to control operation of the motor 22, but may also be used forcontrolling other operations, such as transmit or receive operations forthe transducer array 18. The control wires from the controller 24 extendthrough the housing 11 for connection with the motor 22. Separatecabling may be provided for the transducer array 18 for transmit andreceive operation. Since the rotation of the transducer array 18 islimited, the cabling for transmit and receive operations may connectdirectly with the flexible circuit or the transducer array 18. In oneembodiment, the controller 24 is a mechanical torsional resonantcircuit. The controller 24 is operable to cause the motor 22, shaft 20and ultrasound transducer array 18 to rotate or oscillate about thelongitudinal axis over an arch. In one embodiment, the rotation is overa 270 degree range or less, but greater rotation may be provided. In oneembodiment, the shaft 20 is oscillated to rotate the transducer arrayabout an arc of 20 degrees or less, such as 10 or fewer degrees to eachside of neutral. The housing 11 twists along the flexible section 14 inopposite direction sequentially in response to the oscillation. Inalternative embodiments, the controller 24 causes movement orrepositioning of the transducer array 18 without oscillation.

FIG. 3 shows one embodiment of a method for scanning a volume with anultrasound catheter. The method uses the catheter 10 and associatedsystem shown in FIGS. 1 and 2 or a different catheter. Additional,different or fewer acts may be provided, such as providing acts 30 and32 without acts 34, 36, and/or 38.

In act 30, the transducer array and a portion of the housing of theultrasound catheter are rotated about the longitudinal axis of thecatheter. Both the portion of the housing and the transducer arrayrotate substantially a same amount. Some difference in rotation mayresult from a slippage between the transducer array and the transducersection 12. A shaft within the housing rotates. The shaft is connecteddirectly or indirectly with the portion of the housing, the transducerarray or both the portion of the housing and the transducer array tosupply torque. In response to a motor driving the shaft, torque isapplied to the transducer array. The rotational motion is over any rangeof freedom, such as being less than 360 degrees. For example, thetransducer array is only rotated within an arc about the longitudinalaxis of 30 or fewer degrees. Other lesser or greater amounts of rotationmay be provided.

In act 32, another portion of the housing is twisted about thelongitudinal axis in response to rotation of the transducer array, theportion of the housing connected to the transducer array or both. As aresult of the twisting, a more distal portion of the housing rotatesfurther than a more proximal portion of the housing. For example, aportion of soft or softer material than other portions of the housing 11twists to a greater extent closer to the transducer than a portionfurther away from the transducer. The soft portion of the housingabsorbs at least some of or all of the rotation by twisting. The amountof twisting corresponds to the amount of rotation, such as being thesame. In one embodiment, the greatest extent of twisting is 15 degreesin one direction. Twisting is provided in an opposite direction for agreatest extent of 15 degrees, providing at a 30 degrees of arc. Thehousing is free of twisting or neutral at zero degrees. Asymmetricalamounts of twisting may be provided in alternative embodiments.

The twisting is associated with oscillation in one embodiment. Anultrasound transducer is oscillated about a particular angular position,such as an angular position associated with the neutral position of thehousing 11. In response to the oscillation of the ultrasound transducer,twisting is performed in opposite directions. The twisting is providedalong a straight or bent portion of the catheter. For example, thecatheter curves to conform to a path of a vessel. The twisting isperformed along the longitudinal axis as it curves through the vessel.

In act 34, a portion of the housing of the catheter is maintainedsubstantially free of twisting during the rotation and twisting of otherportions of the housing. For example, a portion of the housing adjacentto the motor is maintained relatively free of twisting where theflexible section between the motor and the transducer array absorbs thetwisting caused by the rotation of the transducer array. In oneembodiment, the motor is positioned within the catheter spaced away froma handle so that the twisting is mostly transmitted along a portion of acatheter spaced away from the handle. Alternatively, twisting istransmitted along a majority of the catheter, such as to a portionexternal to the patient. Where the motor is positioned in a tip portion,the twisting is substantially, entirely or mostly isolated to the tipportion.

In act 36, the ultrasound transducer is used to scan along a pluralityof planes. Using electronic or mechanical steering, acoustic energy issequentially transmitted along a plurality of scan lines within a plane.Since different scan lines are transmitted at different times, the planescanned is a general plane that may allow for some movement of thetransducer array during the planar scan. A plurality of planes isscanned at different positions of rotation about the longitudinal axis.Using controlled movement of the motor or sensing a position of thetransducer array, the relative locations of data associated with thedifferent planes is obtained. As the transducer array moves or rotates,additional data is obtained.

In act 38, an image representing a volume is generated as a function ofdata acquired along the plurality of planes. Using the relative positionof the scan lines or planes, data is interpolated or otherwise used togenerate a three-dimensional representation. For example, data isinterpolated to a three-dimensional Cartesian grid and then volumerendering is performed. In alternative embodiments, one or moretwo-dimensional images associated with a same or different plane aregenerated. For example, the catheter is positioned adjacent to tissue tobe ablated. The transducer array is then rotated until the desiredtissue is identified. Once identified, the position of the ultrasoundtransducer relative to the desired tissue is maintained by ceasingrotation or continuing rotation to counteract any movement of thecatheter.

While the invention has been described above by reference to variousembodiments, it should be understood that many changes and modificationscan be made without departing from the scope of the invention. It istherefore intended that the foregoing detailed description be regardedas illustrative rather than limiting, and that it be understood that itis the following claims, including all equivalents, that are intended todefine the spirit and scope of this invention.

1. A catheter for ultrasound imaging of a volume, the cathetercomprising: a transducer section of the catheter housing an ultrasoundtransducer array, the ultrasound transducer array connected with thetransducer section; a motor section having a motor spaced from thetransducer section; a drive shaft connected with the motor and with thetransducer section or ultrasound transducer array; a flexible section ofthe catheter connected between the transducer section and the motorsection; wherein the drive shaft extends through at least a portion ofthe flexible section, the drive shaft operable to rotate the ultrasoundtransducer array and connected transducer section substantially about alongitudinal axis of the catheter in response to force from the motor,and the flexible section operable to twist about the longitudinal axisin response to the rotation of the transducer section while the motorsection remains substantially free of rotation.
 2. The catheter of claim1 wherein the transducer section connects with the ultrasound transducerarray fixedly such that the transducer section rotates with theultrasound transducer array in resp6nse to force from the motor.
 3. Thecatheter of claim 1 wherein the transducer section is harder than theflexible section.
 4. The catheter of claim 3 wherein the transducersection and the flexible section comprise a same extruded material. 5.The catheter of claim 1 wherein the transducer section and the flexiblesection comprises polymer material.
 6. The catheter of claim 1 whereinthe motor is a micro-motor positioned within a motor section of thecatheter, the flexible section between the motor and transducersections, the flexible section operable to twist about the longitudinalaxis more than the transducer and motor sections in response to theforce.
 7. The catheter of claim 6 wherein the motor section is harderthan the flexible section.
 8. The catheter of claim 1 wherein theflexible section is operable to twist more than the transducer sectionin response to the force.
 9. The catheter of claim 1 wherein theultrasound transducer array is operable to rotate only less than 360degrees around the longitudinal axis in response to the force from themotor.
 10. The catheter of claim 1 wherein the ultrasound transducerarray comprises elements extending along the longitudinal axis, therotation of the ultrasound transducer array operable to rotate animaging plane of the ultrasound transducer array about the longitudinalaxis.
 11. A system for ultrasound imaging of a volume, the systemcomprising: a catheter having a housing; an ultrasound transducer arrayof elements within the housing; and a shaft within the housing, theshaft connected with the ultrasound transducer array of elements theultrasound transducer array operable to rotate about a longitudinal axisof the housing in response to rotation of the shaft, and the housingoperable to twist between a first portion and a second portion of thehousing, an amount of twist corresponding to an amount of rotation ofthe ultrasound transducer array; wherein the ultrasound transducer arrayis connected to the second portion such that the second portion of thehousing rotates with the ultrasound transducer array and the firstportion is substantially free of rotation.
 12. The system of claim 11further comprising a motor within the first portion, the motor operableto cause the rotation of the shaft.
 13. The system of claim 11 whereinthe housing comprises a third portion between the first and secondportions, the third portion having a lower durometer than the firstportion.
 14. The system of claim 11 wherein the ultrasound transducerarray is operable to twist only less than 360 degrees around thelongitudinal axis in response to the force from the shaft.
 15. Thesystem of claim 11 wherein the shaft is more rigid than the housingbetween the first and second portions.
 16. The system of claim 11wherein the elements extend along the longitudinal axis, the rotation ofthe ultrasound transducer array operable to rotate an imaging plane ofthe ultrasound transducer array about the longitudinal axis.
 17. Thesystem of claim 11 further comprising: a motor connected with the shaft;and a controller operable to cause the motor to oscillate the shaft;wherein the ultrasound transducer array is operable to oscillate aboutthe longitudinal axis over an arc less than 270 degrees in response tothe oscillation of the shaft, the housing operable to twist in oppositedirections sequentially in response to the oscillation.
 18. The systemof claim 17 wherein the housing comprises Pebax.
 19. The catheter ofclaim 1 wherein the drive shaft connects with the motor through a speedreduction mechanism operable to convert rotational motion to lateralmotion and back to rotational motion.
 20. The system of claim 12 whereinthe shaft connects with the motor through a speed reduction mechanismoperable to convert rotational motion to lateral motion and back torotational motion.
 21. A system for ultrasound imaging of a volume, thesystem comprising: a catheter housing having a first, second and thirdportions; an ultrasound transducer array of elements within the firstportion of the housing; a shaft within the housing, the shaft connectedwith the ultrasound transducer array of elements, the ultrasoundtransducer array configured to rotate about a longitudinal axis of thehousing in response to rotation of the shaft, the first portion of thehousing configured to rotate with the ultrasound array, and the secondportion of the housing configured to twist while the first portion ofthe housing rotates and the third portion remains substantially free ofrotation.
 22. The catheter of claim 1 wherein the motor is within aportion of the catheter operable to be inserted within a patient.